Surface rolling effect on effective short fatigue cracks density, which reflect the affecting capacity on the initiation firstly and then growth of the dominant short crack result finally in specimen failure, is experimentally studied by a replica technique. Two groups of smooth hourglass shaped specimens of LZ50 axle steel with/without rolled surfaces were tested. The crack density of surface rolled specimens was much lower than that of the other group. This indicates surface rolling technology having the effect of hardening surface layer material to introduce compressive residual stresses. The effect appears to restrain the short crack nucleation and propagation and then, to extend the fatigue life.